The Spaniard, who won Europe’s only Senior Major Championship at St Andrews in 2018, mixed six birdies with one bogey in wet and windy morning weather to card a six-under 65 and set the early pace at five under.
Despite more favourable conditions for the afternoon starters, nobody could catch Jiménez with fellow two-time Senior Major champion Alex Cejka and American Mario Tiziani – brother-in-law to Steve Stricker – his nearest challengers after they recorded 68s.
Jeev Milka Singh sits in a tie for fourth place alongside Vijay Singh at two under, with 2016 champion Paul Broadhurst and Paul Lawrie in a group of seven players one shot further back after they opened with a 70 in Wales.
Jiménez – a 21-time DP World Tour winner – recorded six top-20 finishes at The Open earlier in his career and is still relishing links golf at the age of 59.
“It’s my favourite major and playing in these conditions on this golf course, Royal Porthcawl is a great links,” he said.
“I really enjoy playing links, love it.
He added: “I played very solid, all parts of the game. I finished with a birdie on the last hole, hit a beautiful drive and seven iron second shot.
“The only bad shot I hit was on hole 14, my second shot with a four iron.
“I was rushing myself probably there, and I just pulled it left and didn’t make the up-and-down there. That’s really the only bad thing. I am happy.”
Cejka finished in a tie for ninth at the US Senior Open earlier this month and he brought that form with him as he registered one of only two bogey-free rounds all day alongside Lawrie.
The 52-year-old German made birdies at the first, sixth and 14th but was unable to add further gains down the stretch on a day in which only three holes played under par.
“I played well,” said the 52-year-old. “I hit a lot of good tee shots. Played kind of smart. Tried to avoid the bunkers. Tried to avoid the high stuff and hit a lot of good shots.
“It’s not easy. We were maybe a little bit lucky with the weather. The morning wave, it was raining a little bit, a little bit more wind I think.
“But we kind of had a really nice day. It was blowing but nobody likes to play in the rain. So it’s been good.”
Tiziani, playing in the third from last group of the day, made his fifth birdie of the round on the final hole to join Cejka two shots off the pace as he bounced back from bogeying his opening two holes to make an impressive start on his Senior Open debut.
Milka Singh was another from the afternoon wave to enjoy the kinder conditions as he played his first ten holes in three under par.
Despite the setback of back-to-back bogeys at the 14th and 15th, he closed out the day with a birdie after wonderful approach into the 18th green set up a chance for an eagle.
Milka Singh later revealed how his first ever experience of links golf was at Royal Porthcawl as a 15-year-old.
“We were playing the Indo French Championship in Paris,” he recalled. “Didn’t have a visa for the U.K. Last minute, decided that we wanted to play the British Amateur qualifier.
“Get to the British embassy, they said, no, you’ve got to go back to your home country to get the visa. So it was three of us, and we called up Sir (Michael) Bonnalack. He was kind enough to call the embassy up. Got us the visa, but for those three days, we barely had money to survive.
“So we lived on the street, basically. One night we slept under the Eiffel Tower. The next night, we were in a train but cops came and they said, you need to be out. The train station closes at 1.00am and it opens at 5.00am.
“So for four hours we are just roaming around. We used to sit on the train at 5.00, go from one corner to the other corner till we got – to the embassy opened at 10.00, got there, got a visa, got here, and that was the first time I played a links course. That was Royal Porthcawl. I was 15 years old, got to this golf course, the first day. I said, oh, this is easy golf, there’s no wind.
“Next day, the wind blew, I said, how do they play golf in this? That was it. I didn’t qualify. And here I am, after so many years, I think 38 years afterwards, I’m playing the Senior Open at Royal Porthcawl.”
The Indian was later joined by former World Number One Singh who cancelled out two birdies with two bogeys before he finished his round in style with one of nine eagles recorded at the par-five 18th.
Broadhurst made a blistering start with four birdies in his opening seven holes, before dropping three shots in a six-hole stretch from the ninth.
In contrast, 1999 Open Champion Lawrie was a consistent force all day as he made one lone birdie at the par-five sixth in addition to 17 pars.
The British duo sat alongside Kiwi Steven Alker, American Tom Gillis, Italy’s Michele Reale, Sweden’s Jarmo Sandelin and South Africa’s Keith Horne in a share of sixth place at the end of the day.
Home hope Bradley Dredge was in an six-strong group at level par on his Legends Tour debut, having turned 50 earlier this month.
Defending champion Darren Clarke opened with a two-over 73, which was matched by Bernhard Langer who has won on the Senior Open’s previous two visits to Royal Porthcawl.
